Get Date from Date DataType in ASP.Net

Dear All, 

I HAVE USER TABLE TO ragister user .

i want to insert current date into table when user insert for get every 30 days get data previos 30 date data from date 

so please give me suggest which datatype is used for this to complete these task 

i have date datatype but when we insert date   DateTime.Now.ToString("yyyy-MM-dd");

date insert into database 

6/1/2018 12:00:00 AM

and i not want to timespan 

thanks in advance